If you were the supreme ruler of the world, what would you do to change the realtionship between Mexico and the United States?

If I was the supreme ruler of the world and had to change the relationship between Mexico and the United States, I would do many things I'm sure. But what I can think of now, is this: I would do my best to make the country, Mexico, understand the importance of immigrating legally. I would also fix their corrupt government so that illegal immigration would not be such a problem in the first place. After that, I would make the United States/Mexico border stronger to protect us from harms. But with changes in Mexico's government, I think that illegal immigration would not be such a problem anyways. This was a hard question because in my opinion, these things happening are as likely as me being Supreme Ruler of the World.